The present invention relates generally to gyroscopes for determining angular rates about a sensitive axis as required by an inertial guidance and navigation system of an aircraft: and more particularly to an improved gyroscope apparatus which utilizes the phase coherence of Cooper-paired electrons to measure the rotation of a platform.
Conventional guidance and navigation systems generally include a gyro-stabilized platform to measure the rate of angular motion of a vehicle. Early systems included an electrically driven rotor in one or two sets of gimbals mounted on the vehicle. Due to inaccuracies produced by friction between the moving parts, temperature changes and inadequate manufacturing tolerances, other devices have evolved which have no moving parts. In a nuclear gyroscope, for example, the spinning mass is replaced by the spin of atomic nuclei and electrons.
The current trend in non-mechanical sensors is the ring laser gyro (RLG). It consists of a resonant optical cavity on a platform and contains two laser beams traveling in opposite directions in a triangular or square shaped path formed by three or four mirrors. With the gyro at rest, the two beams have the identical frequency, but when rotated about its sensitive axis, the frequency of one beam decreases while the frequency of other increases. The frequency difference .DELTA.f is a direct function of the angular rate of rotation, which is: EQU .DELTA.f=4A.omega./L.lambda. (1)
where:
A=area enclosed by the optical path; PA1 .omega.=angular rate of rotation of the platform; PA1 .lambda.=transition wavelength of the laser beam; and PA1 L=the optical path length.
The RLG is limited in its ability to measure applied rates more accurately by its mechanical dither and the spontaneous emission from the laser. Both mechanisms contribute to a random wander term in the output signal. Attempts to eliminate the dither motor have not proven successful. It is for these reasons that new technologies are being investigated to develop instruments with improved sensitivity.
The discovery of high temperature superconducting materials has spurred new interest in developing a gyroscope utilizing their unique properties. Recent studies include the London moment gyroscope to verify in earth's orbit two small precessional effects predicted by the theory of general relativity, the geodetic and Schiff motional effects. See, Anderson, J. T. et al, Development of a London Moment Readout for a Superconducting Gyroscope, American Institute of Physics (1978). A niobium-coated quartz sphere is electrostatically suspended, cooled to below the transition temperature, and spun in a vacuum. The magnetic moment of the sphere--the London moment--is aligned with the spin axis and the current in a readout loop is indicative of any change in orientation. The Barnett moment gyroscope is another sensor under study for use in navigation systems. It utilizes the same principles as the London moment except it is a cylinder with .mu.-metal in the core to exhance the magnetic field intensity. Neither of these concepts, however, have reached the point of practicality as a substitute for gyros presently in use.